harder "metal" (like the metal jacket on a kiln) or did you mean harder soft brick? if so, this is because it's got a refractory mortar/coating on it, and it's just a coating. beyond this is soft brick which is easily cut with pretty much any saw.

if it's metal - i would use a standard cutoff wheel (not diamond) on the metal to get through the jacket, then switch to a sawzall or hand saw (or even hole saw) for getting through the soft brick.

removing the lid and putting it on surface that will absorb vibrations will be smart as well. good luck!

So I have an electric kiln that i am converting to gas and I need to cut a chimney in the top. The top is a harder metal not your typical electric kiln soft metal. How should I go about cutting it

Since you only asked about metalI'm assuming it stainless steel-but thats not over the lid top usually unless its an old square cress or other brand. The soft brick will cut like butterI do agree on Perkos standard cutoff wheel suggestion.That should cut just about anything.Wear eye and ear protectionMark

So I have an electric kiln that i am converting to gas and I need to cut a chimney in the top. The top is a harder metal not your typical electric kiln soft metal. How should I go about cutting it

Since you only asked about metalI'm assuming it stainless steel-but thats not over the lid top usually unless its an old square cress or other brand. The soft brick will cut like butterI do agree on Perkos standard cutoff wheel suggestion.That should cut just about anything.Wear eye and ear protectionMark

yeah, cutoff wheel on a grinder will cut through that thin sheet metal like butter. if you don't want the hole in the brick exactly where your hole in the jacket is at, you can try to score the metal with the grinder (if you have the dexterity) until you just barely make it through, then cut your brick hole wherever you want. either way, should be easy.

i doubt the metal will be easily separated from the kiln - age and fatigue from heat cycles will make it difficult and most likely brittle. i'd leave it in place for this task.

Cut thru the metal larger hole than you need so metal is not near exhaust hole. Then with hole saw (hand saw) cut the bricks. Those old cress kiln are build like tanks-weigh a ton and last forever.
Mark